1. Field of the Invention
The present invention relates to an information processing apparatus having a function of displaying a plurality of graphs and, more particularly, to an information processing apparatus having a function of displaying a plurality of graphs wherein a plurality of graphs are drawn one over the other on the same screen such as scientific electronic calculators, electronic notebooks, personal computers, and word processors.
2. Description of the Related Art
In this type of information processing apparatuses, to display two graphs representing different functions on one screen, the horizontal and vertical axes have been graduated in association with the two function graphs and have been shared by the graphs.
FIG. 10 illustrates an example of the display of graphs on a conventional information processing apparatus having a function of displaying a plurality of graphs. An example of full-span display of a function "Y=25 cos X" on a graphic screen is shown at (a) in FIG. 10 where the maximum value Ymax and minimum value Ymin of the vertical axis are set to 25 and -25, respectively, and the maximum value Xmax and minimum value Xmin of the horizontal axis are set to 200 and -200, respectively.
An example of full-span display of a function "Y=sin X" on the graphic screen is shown at (b) in FIG. 10 where the maximum value Ymax and minimum value Ymin of the vertical axis are set to 1 and -1, respectively, and the maximum value Xmax and minimum value Xmin of the horizontal axis are set to 200 and -200, respectively.
An example of display of the function "Y=sin X" at (b) in FIG. 10 on the graphic screen is shown at (c) in FIG. 10 where the vertical axis is set to the same scale as that of the vertical axis shown at (a) in FIG. 10 (Ymax=25, Ymin=-25).
An example of overlapped display of the function "Y=25 cos X" at (a) in FIG. 10 and the function "Y=sin X" at (c) in FIG. 10 on the graphic screen is shown at (d) in FIG. 10 where the vertical axis is set to the same scale as that of the vertical axis shown at (a) in FIG. 10 (Ymax=25, Ymin=-25). In this case, the graph of the function "Y=sin X" shrinks and becomes very unclear.
As apparent from the example of display of a graph shown at (d) in FIG. 10, when graphs having greatly different display ranges are drawn to the same scale, one of the graphs shrinks. For example, this makes it impossible to know the shape of the graph which has shrunk even if the trace pointer (trace mark) is moved to trace the graph, which has resulted in a problem in that the comparison of those graphs becomes very difficult.
Although tracing functions are available in the prior art and are substantially similar to each other, there has been a problem associated with the comparison of graphs because, for example, no function has been available to change the scale of the vertical axis in association with a plurality of graphs.
As another example of the prior art, there has been proposed a graph creating device for generating a Pareto diagram from a plurality of common data to be graphed wherein a plurality of bar graphs (items) having predetermined widths are drawn along one of the axes of a polygonal line graph and wherein the polygonal line graph is synthesized with the plurality of bar graphs by overlapping them with the positional relationship between the polygonal line graph and the widths of the bar graphs varied arbitrarily (see Japanese Unexamined Patent Publication HEI 5(1993)-250484).
As another example of the prior art, there has been proposed a process monitoring apparatus for displaying a plurality of trend graphs on the same screen at a time wherein the scale is appropriately graduated from the upper and lower limits of process values; scales and scale values are assigned with the length of the scale axes adjusted to in relation to the upper and lower limits of the process value; and the horizontal axis is displayed in the trend display range inside the upper and lower limits of the scale (see Japanese Unexamined Patent Publication HEI 4(1992)-306696).
As still another example of the prior art, there has been proposed a compact electronic calculator having a function of displaying graphs wherein, when data for displaying a graph is provided in such a manner that it overlaps data for displaying a graph preset in a display storage means, the former is overwritten without clearing the latter to display the plurality of graphs in an overlapping relationship (see Japanese Unexamined Patent Publication SHO 61(1986)-256380).
According to Japanese Unexamined Patent Publication HEI 5(1993)-250484, a Pareto diagram is created by changing the positional relationship between a polygonal line graph and bar graphs arbitrarily to improve the clarity of the correspondence between the points of transition on the polygonal line graph and the bar graphs. However, there is no means for finding the correspondence between the scales on the axes and the polygonal line graph. Therefore, to determine the characteristics of a Pareto graph, it is necessary to visually trace the polygonal line graph and the bar graphs of interest from the scale for the determination of the characteristics of the Pareto diagram. This has limited the-readability of such a Pareto diagram.
According to Japanese Unexamined Patent Publication 4(1992)-306696, a process monitoring apparatus is improved in that the determination of upper and lower limits of the process value becomes easy because a plurality of trend graphs can be displayed on The same screen at a time with the positions of graduations on the scale axes thereof adjusted for each of the trend graphs. However, no representation means is provided to identify correspondence between the trend graphs and scale axes. Therefore, readability is not approved when the value of a transition on one particular trend graph is to be read.
Further, according to Japanese Unexamined Patent Publication SHO 61(1986)-256380, it is possible to simultaneously display a plurality of graphs on the same screen one over the other without clearing graph displaying data which has been preset in a display storage means. Although this simplifies procedures for inputting graphs, there is no provision for display of graphs along two types of axes having different scales that depend on the graphs. For example, this results in a problem associated with the display of two mathematical expressions in that, when graphs having ranges greatly different from each other are drawn using the same scale, one of the graphs is compressed or expanded beyond the full scale
Assume that a plurality of graphs spanning different ranges are displayed about the X axis serving as a common axis with a plurality of scales provided along the Y-axis.
As described above, there is no representation means for identifying the correspondence between the graphs and the scales according to the prior art. This has resulted in a problem in that, when the shape or the value of a transition in a particular graph is to be read, a wrong scale may be used and the value of a transition may be difficult to read.